Stray voltage: the invisible and “hard to explain” situation that can occur on and around electric fences. I don’t know how many questions, phone calls and emails I have received over the years that have ultimately been a result of stray voltage – but there have been a lot of them.
Electric fences are typically charged with very short low current and high voltage pulses. These pulses (on low impedance chargers) are generally less than 3/1000’s of a second in duration. This is much different that the continuous current that is flowing through the wires in your home, which are high current and low voltage.
A majority of problems that people have with electric fences are because they forget about or don’t understand the basic principles of electricity. When electricity is sent out on an electric fence by an energizer it doesn’t just mysteriously disappear into thin air. What goes out ultimately must come back. And, it seems to be continually seeking a ground to complete its circuit.
Normal house type wiring, which has an insulation rating of 600 volts, should not be used for electric fencing. The voltage on a fence wire is typically around 6000 volts and capable of 10,000 volts. The high voltage on the wire can easily find its way to ground through the insulation of normal house type wiring.
But unlike electric wires, in your home or barn that is kept in nice clean insulated wires, the electricity that is cycling down your fence wire and through the environment can end up going places it was never intended or meant to go. Some thought needs to be put into setting up both a well insulated conducting system, and an adequate earth return system.
Since your fence wire is the conductor, it is bare wire and is not wrapped up with insulation like a strand of house wiring. It must be bare to transfer a shock to an animal that touches it. The electric pulse that flows down the wire is actually flowing down and around the perimeter of the wire. This creates somewhat of a field of electricity – in my layman’s terms. Have you ever seen an animal approach an electric fence and walk up to it with its nose still a foot away and then back off? I “think” that’s because of the sensitivity of the animal’s nose along with long hair follicles, that they feel a little tickle, before they actually touch it. Goats in particular, are very acute to sensing if there is electricity flowing down that wire, before they ever touch it.
This also happens in a lot of unlikely places, such as around a metal gate. Have you ever got a shock from a metal gate (within an electric fence system) that had no actual power attached to it? I have, and it’s not a very desired or pleasant experience.
Sometimes and often, on multi-wire fences where you have alternating hot wires and ground wires – you will read voltage on the non-electrified wires. This is generally stray voltage that has “strayed” off of the hot wire. Is that a bad thing? I guess the answer is it depends. During normal conditions, it probably isn’t all that bad of a thing, but during wet damp weather, this condition will suck a lot of power out of your system.
In either of these scenarios an option to capture that stray voltage and get rid of it, is to install a ground rod and direct the stray voltage to ground.
Many times (and usually) stray voltage problems with electric fencing can be traced to either a lack of adequate grounding or poor selection of the grounding site, or a combination of both. Loose or corroded ground rod connections can also attribute to many problems with stray voltage. Let’s talk about these separately.
- Lack of adequate grounding. How many ground rods do you need? Hopefully the energizer manufacturer will have a recommendation in the packaging, but this is not always the case. My personal recommendation (for a minimum) is that you will need 3 feet of rod in the ground, per each output joule of power. Example: you have a 15 output joule charger. You will need 15 x 3 = 45 feet of ground rods in the ground. This will equate to 8 each 6 foot rods or 6 each 8 foot rods. Again, this is minimum and considered to be in good solid moist soil. If it is very dry or gravely, then you will need more. The effective field of a ground rod is a 5 foot radius, so your rods should be spaced at least 10 feet apart. If you put two rods at 3 or 4 feet apart, they will perform as one ground rod.
Testing of the grounding can be done with a regular electric fence digital voltmeter. The ones with a ground probe and a lead with a clip works the best for this. Now, go at least a hundred feet down your fence line away from your energizer and ground rods. Put a load on the fence (create a short) and try to get the fence voltage down to 1000 volts or less (a digital meter reading of 1.0 KV). Now go back to your ground rods and take a reading on the last ground rod. Your goal would be to read “0” volts, however a reading of up to 300 volts would be acceptable (this would read 0.3KV on a digital meter). If you read more than 300 volts, then this is telling you to add more ground rods. In essence you should keep adding rods until you get it below 300 volts.
- Selection of the grounding site: should be a very important consideration, but many times it is chosen by convenience. Firstly, the ground field for your fencing system MUST be located at least 50 feet away from any other utility grounding. This includes power poles, well houses, etc. It should be at least 50 feet away from buried waterlines and various other underground utilities.
The site should be located in a place of permanent moisture. For this reason, the drip line of a building is often used.
Generally most people install their grounding so that it is convenient to the fence charger, but this is not necessary. In fact I know many people that install their ground rods out in the middle of their farm. For example, a fenced off pond that has some seepage may be an ideal place. The downside is the added cost of running a wire back to the energizer, but this can be done rather easily.
- Loose or corroded ground rod connections: should be a no-brainer, but it’s a simple little inspection that we often overlook. I think that it should be on the annual housekeeping list. Ground rod clamps do occasionally break, become loose or get corroded. They need to be checked periodically.
Once a customer called me saying that sometimes when he climbed his ladder on his feed bin, he would get shocked. I went out to the farm on that one, and it turned out that his feed bin was grounded within 6 feet of the ground rods for his fence charger. On wet dewy mornings when he had a heavy fence load he would get stray voltage feeding back thru the separate grounds, basically because they were too close together.
I received an email just the other day regarding what appears to be stray voltage getting into a metal water tank. This was over 1400 miles away, but I did call the waterer manufacturer and they suggested that he turn all power off to the waterer and call a licensed electrician to determine where it was coming from. I’m still waiting to hear about how that one turned out. There was some electric fence nearby as well as a buried waterline.
Another instance was when a fence contractor called me one day, stating that his guys were installing a new high tensile fence and were getting shocked. They had not installed the energizer yet. There was no power on the fence yet. I asked him if there was an overhead power line above the fence – and he said, yes there was. We couldn’t come up with any other possibilities as this was a pretty remote area. Obviously there was stay voltage from the overhead power line getting into the fence. I doubt that the local rural electric would admit to that, but this happens a lot around dairy farms. Or, so I hear, so it may be hearsay…….
Well, here I am up to 1500+ words and still have only scratched the surface of this subject. Research shows that Stray Voltage on Farms has been a problem for the past 50 years and continues to be so. Here is an excerpt from the Midwest Rural Energy Council (see http://www.mrec.org/pubs/StrayVoltage_InformationalPage_05.pdf) that says:
Can we get rid of stray voltage? The laws of physics and the electrical code safety requirements make complete elimination of stray voltage impossible. Stray voltage will always be present at some level. However, properly installed and maintained electrical systems can keep this voltage at a low level that science has shown does not have a negative impact on cattle.
In summary, the major key points for reducing stray voltage on electric fences are:
- The safe use of electricity is dependent on our electrical systems being properly and adequately grounded.
- Placement of grounding must be located at safe distances away from other utility grounds.
- The conductor wire must be installed and maintained with quality non-conductive insulation devices.
And, last but not least – the use of insulated and non-conductive line posts will drastically cut down on possible failures, such as failed or broken insulators and wire attachment devices.